1. Field of the Invention
This invention relates to a method of stabilizing organic substrate materials against the action of light, and more particularly to a method of stabilizing organic dyestuffs to light irradiation.
2. Discussion of the Prior Art
Generally it is well known that many organic substrate materials such as, for example, organic dyestuffs tend to fade or discolor by the action of light. A number of studies on the prevention of such fading and/or discoloration of organic dyes, i.e., on the improvement of light-fastness have been carried out in the related technical fields including printing ink manufacture, textile dyeing and color photography. The instant invention provides a quite effective method for improving the light-fastness of dyes and other organic substrate materials.
In the present specification, the term "organic substrate material" or "substrate material" mean a substance which appears colored or colorless to the human eye under the irradiation of sunlight, inclusive of not only those substances having absorption peaks within the visible spectrum but also those with absorption peaks which lie in the U.V. and infrared regions. An exemplary compound of the latter type is an optical brightening agent. Hence, the organic substrate materials of the instant invention include organic compounds having absorption maxima between about 300 nm in the ultraviolet region and about 800 nm in the infrared region.
These organic substrate materials occur particularly in photographic materials, e.g., color films, prints, diffusion transfer units, etc., in colored polymers useful as a agricultural vinyl cover sheets, umbrellas, tents, etc.; fluorescent whitening agents; and dyed textiles, etc., and this invention is directed to improving the light fastness of these materials in each of these fields.
The term "dye" or "dyestuff" as used in the instant specification means an organic substance which appears colored to the human eye under the irradiation of sunlight.
Further, the term "light" refers to all forms of actinic radiation having wavelengths below about 800 nm, thus including ultraviolet light up to about 400 nm, visible light between about 400 and about 700 nm and infrared light of from about 700 to about 800 nm in wavelength.
With regard to the well-known tendency of organic substrate materials to undergo dye fading or discoloration under the influence of actinic radiation, various methods of improving light-fastness have been proposed. Such methods are exemplified by the one set forth in U.S. Pat. No. 3,432,300 wherein phenol-type compounds having a fused heterocyclic ring structure together are used with substrate materials such as indophenol, indoaniline, azo and azomethine-type dyes to improve the fastness of these dyes to the action of visible and UV light.
In the art of silver halide photographic lightsensitive materials, the oxidation product of an aromatic primary amine developing agent reacts with a coupler to form an azomethine- or indoaniline-type dye, as is described in Chapter 17 of "The Theory of the Photographic Process" authored by C. E. K. Mees and T. H. James (Macmillan Co., 1967). A number of methods for enhancing the stability to light of these photographic dye images have been proposed, including those set forth in U.S. Pat. Nos. 2,360,295, 2,418,613, 2,675,314, 2,701,197, 2,704,713, 2,728,659, 2,732,300, 2,735,765, 2,710,801 and 2,816,028, British Pat. No. 1,363,921, etc., all based on the use of hydroquinone derivatives; those set forth in U.S. Pat. Nos. 3,457,079 and 3,069,262, Japanese Patent Publication No. 13,496/1968, etc., all using gallic acid derivatives; those set forth in U.S. Pat. Nos. 2,735,765 and 3,698,909 using p-alkoxyphenols; those set forth in U.S. Pat. Nos. 3,432,300, 3,573,050, 3,574,627, 3,764,337, 3,574,626, 3,698,909 and 4,015,990, using chroman and coumarane derivatives, etc. However, these customarily known compounds do not exhibit a sufficient degree of fade or discoloration prevention ability.
British Patent No. 1,451,000 discloses a method for stabilizing, organic substrate materials against the action of light using azomethine quenching compounds which have absorption peaks at longer wavelengths than the substrate materials. This method has a serious drawback that the deep color of the azomethine quencher itself deteriorates the color hue of the substrate material.
The use of metal chelate compounds for the purpose of preventing the light-induced degradation of polymers is described in the following papers; J. P. Guillory & R. S. Becker, J. Polym. Sci., Polym. Chem. Ed. 12, pp. 993 (1974), and R. P. R. Ranaweera & G. Scott, J. Polym. Sci., Polym. Lett. Ed., 13, pp. 71 (1975). Metal chelate compounds are also used for the stabilization of dyestuffs as is discolsed in Japanese Patent Application (OPI) No. 87,649/1975 and Research Disclosure 15162 (1976). However, the chelate compounds disclosed in the above literature are not only effective to an unsatisfactory degree, but are provided with too low solubilities in many organic solvents to permit their incorporation into the system at a concentration level high enough to exert the effect of fade prevention. Moreover, most of these chelates are so deeply colored themselves that their presence at higher concentration levels adversely affects the color hue and the color purity of the substrate material (particularly dyestuffs) involved.